/Engine/Plugins/Experimental/GeometryScripting/Source/GeometryScriptingCore/Public/GeometryScript/MeshQueryFunctions.h
For the specified TriangleID of the Target Mesh, get the Normal vectors at each vertex of the Triangle. These Normals will be taken from the Normal Overlay, i.e. they will potentially be split-normals.
static [UDynamicMesh](API\Runtime\GeometryFramework\UDynamicMesh) * GetTriangleNormals ( [UDynamicMesh](API\Runtime\GeometryFramework\UDynamicMesh) * TargetMesh, int32 TriangleID, FVector & Normal1, FVector & Normal2, FVector & Normal3, bool & bTriHasValidNormals )